The present invention generally relates to systems for the recovery of gas and/or heat and conversion thereof to electrical power. More specifically, the present invention relates to systems for recovering gas and/or heat from melting or smelting processes used in the manufacturing and/or refining of metals and/or their by-products. The recovered gas and/or heat is converted into electrical power. More specifically, the heat may be converted to superheated steam through a heat exchanger for operating a turbine and electrical power generator to produce electrical power. Moreover, flue gases from the melting and/or smelting processes used in the manufacturing and/or refining of metals and/or their by-products drive a gas turbine and electrical power generator to produce electrical power.
It is generally known to melt and/or smelt metals and metal ore in the manufacture and/or refining of metals and their by-products. Generally, smelting is a form of extractive metallurgy that is used to remove metals from unprocessed and unrefined ores. This may include, without limitation, iron extraction from iron ore, copper extraction from copper ore and other base metals from their ores, respectively. In general, smelting utilizes heat and a chemical reducing agent, commonly a fuel that is a source of carbon, such as coke (or, in earlier times, charcoal) to change the oxidation state of the metal ore. The carbon source typically removes oxygen from the ore to leave the relatively pure metal. In addition, since most ores have impurities within them, it is often necessary to use flux, such as limestone, to remove rock gangue as slag.
Melting of metals and/or smelting of metal ores takes place in a furnace. Virgin material, external scrap, internal scrap and/or alloying elements are typically used to charge the furnace. Virgin material refers to commercially pure forms of the primary metal used to form a particular alloy. External scrap is material from other forming processes such as punching, forging or machining. Internal scrap consists of the gates, risers and/or defective castings. Alloying elements are either pure forms of an alloying element, like electrolytic nickel, or alloys of limited composition, such as ferroalloys or master alloys.
Several specialized furnaces are used to melt the metal. Furnaces are refractory-lined vessels that contain the material to be melted and provide the energy to melt it. Modern furnace types include electric arc furnaces, induction furnaces, cupolas, reverberatory furnaces and crucible furnaces. Furnace choice is dependent on the alloy system and the quantities produced. For ferrous materials, electric arc furnaces, cupolas and induction furnaces are commonly used. Reverberatory and crucible furnaces are common for producing aluminum castings.
Moreover, furnaces are designed based on several factors, including but not limited to size and the type of metals that are to be melted. Furnaces are further designed around the fuel being used to produce the desired temperature. For low temperature melting point alloys, electricy, propane and natural gas are typically used. For high melting point alloys, such as steel or nickel-based alloys, the furnace must be designed for very high temperatures and typically utilize electricity or coke as the fuel source.
In general with respect to smelting of metal ores, the ores are typically metal oxides and/or sulfides. In a typical first step, the ore or metal is melted and two liquids are formed: one, a slag containing most of the impurities; and two, a sulfide matte containing the metal sulfide, metal atoms in elemental form and some impurities. Fuel is burned during this process, and the heat generated melts the dry sulfide concentrates. The slag floats on top of the heavier matte and is removed, discarded and/or recycled. The matte is then sent to a refiner or a converter for converting to a pure metal.
Slag is a vitreous by-product of smelting ore and melting steel and/or other metals to purify these metals. The bulk of the slag contains impurities, but slag may also contain residual metals. While slags are generally used as a waste removal mechanism, they can also serve other purposes, such as assisting in smelt temperature control and minimizing re-oxidation of the final liquid metal product before casting.
The slag may go through further processing to remove any of the residual metals, and the cooled and separated resulting slag may be utilized as a material, such as a filler and/or aggregate for road construction and/or site construction, for example.
It should be noted that the description herein describes a general process for the production of metals from a melting and/or smelting process; however, other processes may or may not use carbon or coke, or may differ from processes described herein, such as for the production of aluminum. These processes are still referred to as a melting and/or smelting process for purposes of the present invention.
It is also generally known to use steam and hot gases to generate electricity. The so-called “Rankine Cycle” is a thermodynamic process that utilizes water in a closed loop system to convert heat into work. Heat is generated or utilized from a variety of sources to heat water into steam as a working fluid. The steam then drives one or more turbines to generate electricity via an electric generator. The steam then cools and is recycled back to be reheated yet again. The process then continues the cycle as long as there is a fuel to heat the water into steam. It is estimated that approximately 80% of the world's energy production comes from use of the Rankine Cycle.
One source of energy used to convert liquid water to steam to drive turbines to generate electricity comes from geothermal energy sources. For example, steam may be utilized directly from underground sources, such as an underground steam reservoir, or cycled through an underground heat source. When water converts to steam, it rapidly expands, thereby driving a steam turbine and generator to generate electricity. The steam may then be condensed and injected into the steam reservoir or recycled to the heat source. The steam is typically condensed using relatively cool water cycled, there through, where a heat transfer occurs. Another type of power plant is a binary power plant, that pumps heated water from a fuel source to a heat exchanger where a second fluid with a relatively low boiling point, such as butane or pentane hydrocarbon, is vaporized and drives a turbine.
In addition to water, other gases may be utilized to drive a turbine to generate electricity. For example, a fuel source, such as natural gas, hydrogen gas, or the like, may burn in a furnace with the addition of oxygen or air. The rapid expansion of the gas rushes past turbine blades, thereby spinning the turbine blades thereby generating electricity in a generator.
Alternatively, gases may be utilized that are the residual product of a furnace or of a material that off-gasses. These gases may be routed to a turbine to generate electricity.
In a combined cycle process, fuel is burned and gases made therefrom turn turbine blades to generate electricity. The burned fuel then is released into a heat exchanger in a first generator where its heat vaporizes water in conduit into steam. The steam then drives a second turbine to generate electricity in a second generator, where the steam is cooled and condensed and recycled to the boiler in a closed loop system.
It is also generally known to generate hydrogen and oxygen through electrolysis of water. Specifically, an electrical current is passed through water to decompose or hydrolyze the water (H2O) into component molecules of hydrogen (H2) and oxygen (O2). Both hydrogen and oxygen can be utilized in industrial applications. Hydrogen, specifically, can be burned as a fuel.
As noted above, the melting and/or smelting of metals and/or ores to purify the metals utilizes extremely high heat and various reductive chemical reactions. Typically, this heat that is generated to melt and refine the metals and/or ores and form purified metals therefrom is typically wasted. For example, in the melting and/or smelting vessel, heat is utilized to melt the ores to form a liquid metal matte. In addition, hot gases may be produced from the liquid metal matte that are typically lost during the smelting process.
In a typical melting and/or smelting process, water-cooled steel vessels are utilized in the furnace for the melting of metals and/or reduction of metal ore to pure metals. The steel vessels typically have water-cooled panels that form the walls of the steel vessels as well as the roofs of the steel vessels. The panels typically have a plurality of water coils disposed therein circulating water therethrough to keep the melting and/or smelting vessel from melting and to regulate the temperature of the liquid metal and/or slag. The water then circulates to a cooling pond and/or a cooling tower where heat is transferred, thereby cooling the water for recirculating through the panels. Typically, water from the panels can exceed 600 degrees F, whereupon they are delivered to the cooling ponds whereupon they decrease in temperature to enter cooling towers at about 200 degrees F.
Impurities form the slag, which may float on the top of the liquid metal matte in the melting and/or smelting vessel. The slag is also at extremely high temperatures, and is typically removed from the liquid metal matte to undergo further processing in a slag pot to extract any residual metals in the slag. This process produces much heat and off-gassing as well. After the slag is sufficiently processed, it is typically removed from the melting and/or smelting process and disposed in a slag box, for example, and cooled. Much slag is recycled into industrial products, such as road aggregate, fertilizer, cement, and other products.
The liquid metal matte further undergoes refining at high temperatures to form pure or relatively pure metal product. The pure metal product is typically cooled and formed into a shape for transport.
At each stage of the melting and/or smelting process, high heat is generated to institute these steps. Moreover, hot gases are also be off-gassed. In a typical melting and/or smelting process, the heat and gases are typically lost.
A need, therefore, exists for systems for utilizing heat generated during the melting and/or smelting process. More specifically, a need exists for systems for generating electricity from heat generated during the melting and/or smelting process.
Moreover, a need exists for systems for utilizing hot gases from the melting and/or smelting process. More specifically, hot gases generated during the melting and/or smelting process may be utilized to generate electricity in gas turbines.
Further, a need exists for systems for utilizing both the heat generated by a melting and/or smelting process and the gases produced by the melting and/or smelting process. More specifically, a need exists for systems for cogenerating electricity utilizing both the heat and the gases produced during the melting and/or smelting process.
Still further, a need exists for systems for generating power from the heat, the gases, or both the heat and the gases produced during a melting and/or smelting process. More specifically, a need exists for systems for generating electricity from the heat, the gases or both the heat and the gases produced during a melting and/or smelting process.
In addition, a need exists for systems for utilizing electricity generated using the heat, the gases, or both the heat and the gases produced during the melting and/or smelting process. More specifically, a need exists for systems for sending the electricity into a power utility grid or reverse metering the electricity.
Moreover, a need exists for systems for utilizing electricity generated using the heat, the gases, or both the heat and the gases produced during a melting and/or smelting process for the electrolysis of water. More specifically, a need exists for systems for utilizing electricity generated using the heat, the gases, or both the heat and the gases produced during a melting and/or smelting process for generating hydrogen gas, oxygen gas or both hydrogen gas and oxygen gas by the electrolysis of water.